Downhole pump seating nipple with perforations

ABSTRACT

A pump seating nipple for retaining a downhole pump assembly in a fixed position within a production tubing string has a generally cylindrical body defining a nipple bore for receiving the downhole pump assembly. The pump seating nipple attaches to the production tubing string. At the bottom end of the body, the nipple bore is open to the bore of the production tubing string. An upper portion of the body surface engages a pump assembly seating cup. The body has a lower skirt which defines openings which allow gas flow from the nipple bore into the casing annulus.

FIELD OF THE INVENTION

The present invention relates to a pump seating nipple for retaining adownhole pump assembly in a production tubing string of an oil and gaswell.

BACKGROUND OF THE INVENTION

Reciprocating downhole pump systems are used to elevate productionfluids from an oil and gas well to the surface. A typical pump systemincludes a pump jack or other device at the ground surface thatreciprocates an attached sucker rod alternately in upstrokes anddownstrokes. The sucker rod is attached at its bottom end to a plungerthat reciprocates within a hollow pump barrel of a downhole pumpassembly. The plunger includes a travelling valve assembly (e.g., a balland seat valve or a flapper valve) to regulate the flow of a productionfluid from below to above the plunger, while the downhole pump assemblyincludes a standing valve assembly to regulate the flow of theproduction fluid into the barrel from the producing perforations of awell. A retaining device is needed to hold the barrel of the downholepump assembly in a fixed position within the production tubing string asthe travelling plunger moves up and down,

On the upstroke of the plunger, the travelling valve closes, so that theplunger lifts a column of production fluid in the pump barrel, upwardsin the production string, towards the ground surface. Simultaneously,the standing valve is opened so that the plunger draws additionalproduction fluid from the producing perforations of the well into thepump barrel below the plunger. On the downstroke of the plunger, thestanding valve closes to prevent the production fluid below the plungerfrom flowing back into the production tubing. Simultaneously, thepressure exerted by the production fluid in the pump barrel below thetravelling valve forces the traveling valve to open. This allows theproduction fluid to flow into the pump barrel above the plunger andcharges the pump barrel with a new column of production fluid to belifted on a subsequent upstroke.

The performance of the pump system may be adversely affected by aphenomenon known as “gas locking”, This occurs when gases dissolved inthe production fluid breaks out of solution upon entering the relativelylower pressure environment of the wellbore. On the upstroke of theplunger, the gases flow upwards through the open standing valve into thepump barrel between the standing valve and the plunger. On thedownstroke of the plunger, the gases are compressed between the closedstanding valve and the plunger. On the following upstroke of theplunger, the compressed gas in the pump barrel between the travelingvalve and the standing valve expands to fill the enlarged space. Assuch, the upstrokes and downstrokes of the plunger result in therepeated compression and expansion of trapped gas between the standingvalve and the plunger. This interferes with the proper opening of thetravelling valve, and the upward flow of production fluid into thebarrel below the plunger. An associated problem is “fluid pounding,”which occurs when the space in the pump barrel below the plunger ispartially filled with liquid and partially with gas such that theplunger forcefully enters the fluid level part way through thedownstroke. This causes undesired vibrations, or “pounding”, through theproduction tubing string leading to mechanical failure and expeditedwear.

Therefore, there is a need in the art for devices to retain a downholepump assembly within a production tubing string and for devices that mayensure that a traveling valve assembly of a reciprocating downhole pumpsystem opens and closes as intended.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a pump seating nipple forretaining a downhole pump assembly in a fixed position within aproduction tubing string. The production tubing string defines aproduction bore and is disposed within a casing string to define acasing annulus therebetween. The downhole pump assembly conventionallycomprises a resilient seating cup, The pump seating nipple is insertablein the production tubing string and comprises a substantiallycylindrical body having an outer surface, and an inner surface definingan internal nipple bore extending from a top end of the body to a bottomend of the body for receiving the downhole pump assembly at leastpartially therein. The nipple bore is in fluid communication with theproduction bore at the bottom end of the body. The body comprises anupper portion where the nipple bore defines a reduced diameter profileto engage the pump assembly seating cup to resist relative movementbetween the downhole pump assembly and the body and to prevent gasmigration between the downhole pump assembly and the pump seatingnipple. The pump seating nipple body comprises a lower skirt which hasan inside diameter greater than an outside diameter of the pump, andwhich defines at least one opening extending through the skirt for fluidcommunication from the nipple bore to the casing annulus.

In one embodiment, the top end defines a top threaded surface forremovable attachment of the top end to an upper joint, and the bottomend defines a bottom threaded surface for removable attachment of thebottom end to a lower joint.

In one embodiment, the nipple bore is chamfered at either or both anupper end or lower end of the nipple bore profile.

In one embodiment, the nipple bore profile is cylindrical, having asmaller internal diameter than the lower skirt.

In one embodiment, the at least one opening comprises a plurality ofopenings, which may be arranged in a plurality of vertical columnscircumferentially spaced apart on the skirt.

In another aspect, the present invention comprises a downhole assemblydisposed within a casing string. The downhole assembly comprises aproduction tubing string, a downhole pump assembly, and a pump seatingnipple. The production tubing string defines a production bore and isdisposed within the casing string to define a casing annulustherebetween. The downhole pump assembly is disposed within theproduction bore and comprises a barrel with a perforated fitting forfluid communication from the production bore into the barrel, and anattached resilient seating cup. The pump seating nipple is disposed inthe production tubing string. The pump seating nipple comprises asubstantially cylindrical body comprising an outer surface, and an innersurface defining a nipple bore extending from a top end of the body to abottom end of the body for receiving the downhole pump at leastpartially therein. The nipple bore is in fluid communication with theproduction bore at the bottom end of the body. The body comprises anupper portion that engages the seating cup to resist relative movementbetween the downhole pump assembly and the body and to prevent gasmigration between the downhole pump assembly and the body. The bodycomprises a lower skirt which defines at least one opening extendingfrom a lower portion of the inner surface to the outer surface for fluidcommunication from the nipple bore to the casing annulus. In oneembodiment, the at least one opening is disposed above the perforatedfitting.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodimentwith reference to the accompanying simplified, diagrammatic,not-to-scale drawings. Any dimensions provided in the drawings areprovided only for illustrative purposes, and do not limit the inventionas defined by the claims. In the drawings:

FIG. 1 is a sectional, elevation view of a reciprocating downhole pumpsystem incorporating one embodiment of the seating nipple of the presentinvention;

FIG. 2 is an expanded view of the portion of the system shown in FIG. 1between lines A-A and B-B of FIG. 1;

FIG. 3 is a sectional, elevation view of the embodiment of the pumpseating nipple of the present invention shown in FIG. 2; and

FIG. 4 is a photograph showing an external elevation view of analternative embodiment of the pump seating nipple of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a pump seating nipple for retaining adownhole pump assembly in a production tubing string. When describingthe present invention, all terms not defined herein have their commonart-recognized meanings. To the extent that the following description isof a specific embodiment or a particular use of the invention, it isintended to be illustrative only, and not limiting of the claimedinvention. The following description is intended to cover allalternatives, modifications and equivalents that are included in thespirit and scope of the invention, as defined in the appended claims.

FIGS. 1 and 2 show an embodiment of a reciprocating downhole pump system100 incorporating one embodiment of the pump seating nipple 10 of thepresent invention. The pump system 100 includes production tubing string102 defining a production bore 103. The production tubing string 102 ispositioned inside the casing string 104 of a well bore, to define acasing annulus 105 therebetween, The pump seating nipple 10 forms partof the production tubing string 102 between an upper joint 106 and alower joint 108. In the embodiment shown in FIGS. 1 and 2, the lowerjoint 108 is a tail joint terminating near the perforated zone of aformation that produces production fluid F. A packer 110 seals thecasing annulus 105 to prevent upward flow of the production fluid F,thus diverting the production fluid F to flow upwards into theproduction tubing string 102.

A downhole pump assembly disposed within the production tubing string102 includes a barrel 114 with a perforated fitting 112 and a standingvalve assembly (not shown) that regulates the flow of production fluid Finto the barrel 114. A motor 118 at the ground surface is attached to asucker rod 120, which is in turn attached to the top end of a travellingplunger 122 having an internal travelling valve assembly (not shown), Asthe travelling plunger 122 moves alternately in upstrokes anddownstrokes within the barrel 114, the standing valve assembly andtravelling valve assembly open and close in a coordinated manner so thatthe travelling plunger 122 lifts production fluid F through the standingvalve into the barrel 114, and up through the barrel 114 and theproduction tubing string 102 towards the ground surface.

While the plunger 122 reciprocates up and down within the barrel 114,the pump seating nipple 10 holds the downhole pump assembly in a fixedposition within the production tubing string 102. In the embodimentshown in FIGS. 1 and 2, the downhole pump assembly has three externallyattached annular seating cups 116 a, 116 b, 116 c. Seating cups 116suitable for use with pump seating nipples are known in the art and arecommercially available. The seating cups 116 have an external diameterthat is larger than the external diameter of the remainder of thedownhole pump assembly, so that only the seating cups 116 contact aninternal surface of the pump seating nipple 10 when the downhole pumpassembly is positioned in the production tubing string 102. The seatingcups 116 are made of a resilient material and thus bias themselves intosealing engagement with the surrounding inner surface of the pumpseating nipple 10. Friction between the seating cups 116 and the innersurface of the pump seating nipple 10 are sufficient to resist thetendency of the downhole pump assembly to move vertically in response toforces imparted by the movement of the travelling plunger 122.

FIG. 3 shows a cross-sectional view of one embodiment of the pumpseating nipple 10 of the present invention in greater detail. The pumpseating nipple 10 may be made of any suitably hard and durable materialfor use in a downhole environment such as, without limitation, astainless steel alloy.

In general, the pump seating nipple 10 comprises a substantiallycylindrical body. The body has a top end 12 that attaches to the upperjoint 106 of the production tubing string 102, and a bottom end 14 thatattaches to the lower joint 108 of the production tubing string 102. Theattachment of the body to the upper joint 106 and the lower joint 108may be either direct or indirect, and either permanent or removable. Inone embodiment as shown in FIG. 3, each of the top end 12 and the bottomend 14 define a threaded surface for a direct removable connection to acompatible threaded connection formed on the upper joint 106 and thelower joint 108, respectively. In embodiments (not shown), the threadedsurfaces of the top end 12 and the bottom end 14 may be formed on eithera pin-style or box-style connection, wherein an external shoulder of thetop end 12 and the bottom end 14 sealingly abuts an external shoulder ofthe upper joint 106 and the lower joint 108, respectively. Inembodiments (not shown), the body may be attached to the upper joint 106or the lower joint 108 by threaded collars.

The pump seating nipple 10 has an outer surface 16 and an inner surface18. The outer surface 16 is exposed to the casing annulus 105. The innersurface 18 defines a nipple bore 20 extending from the top end 12 to thebottom end 14 that receives at least part of the downhole pump assembly.In one embodiment as shown in FIGS. 1 and 2, the nipple bore 20 permitsthrough passage of the downhole pump assembly upon application of adownward force to the downhole pump assembly sufficient to overcome thefriction between the seating cups 116 and the inner surface 18 of thebody.

The body (10) has an upper portion 22 that defines an upper portion 24of the nipple bore 20, and a lower skirt portion 26 that defines a lowerportion 28 of the nipple bore 20. The upper portion 24 of the nipplebore 20 has an internal diameter less than an external diameter of theseating cups 116 attached of the downhole pump assembly so that theresilient seating cups 116 can be forcibly pushed into the nipple bore20, and expand to engage the upper portion 22 of the inner surface 18.

The lower skirt 26 of the body has an inside diameter which is greaterthan the outside diameter of the pump assembly, and which defines atleast one, and preferably a plurality of openings 30 that extend throughto the outer surface 16, providing fluid communication to the casingannulus. The openings 30 permit gas to escape from the nipple bore 20into the casing annulus 105. Although the shape and configuration of theopenings is not an essential aspect, in one embodiment as shown in FIG.3, the openings 30 have a rectangular shape and are arranged in fourvertical columns of four openings 30, with the columns spacedcircumferentially around the body at an angular separation of ninetydegrees from each other. In an alternative embodiment as shown in FIG.4, the openings 30 have a circular shape and are arranged in fourvertical columns of five openings 30, with the columns spacedcircumferentially around the body at an angular separation of ninetydegrees from each other. In other embodiments (not shown), the shape,number and arrangement of the openings 30 may be different. Theeffective total opening size may be varied by varying the number andsize of the openings.

In one embodiment as shown in FIG. 3, the lower skirt 28 of the nipplebore 20 has an internal diameter greater than the internal diameter ofthe upper portion 24 of the nipple bore 20. The enlarged diameter of thelower portion 28 of the nipple bore 20 relative to the upper portion 24of the nipple bore 20 allows the inner diameter of the upper portion 24of the nipple bore 20 be within very close tolerances (e.g., fractionsof an inch) of the external diameter of the seating cups (116), which isonly slightly larger (e.g., fractions of an inch) than the externaldiameter of the barrel 114, while still allowing for upward flow ofgases within the lower skirt 28 of the nipple bore 20.

In one embodiment as shown in FIG. 3, the body defines an upper chamfer32 between the top end 12 of the body and the upper portion 22 of theinner surface 18. Similarly, the body defines a lower chamfer 34 betweenthe upper portion 22 of the inner surface 18 and the lower skirt 26 ofthe inner surface 18. The chamfers 32, 34 facilitate downward and upwardpassage, respectively, of the downhole pump assembly into the nipplebore 20.

The use and operation of the embodiment of the pump seating nipple 10shown in FIGS. 1-3 is now described. During the completion of thewellbore, the pump seating nipple 10 is attached the lower joint 108 andthe upper joint 106 of the production tubing string 102 and lowered intothe casing string 104. After the production tubing string 102 has beensecured within the casing string 104, the downhole pump assembly islowered into the production tubing string 102. When the downhole pumpassembly reaches the depth of the pump seating nipple 10, it is forciblypushed downwards against the pump seating nipple 10. The resilientseating cups 116 attached to the downhole pump assembly are therebyguided and compressed by the upper chamfer 32 into the nipple bore 20.The seating cups (116), by virtue of being compressed by the upperportion 22 of the inner surface 18, bias outwardly into sealingengagement with the upper portion 22 of the inner surface 18. Frictionbetween the inner surface 18 and the seating cups 116 resist relativevertical movement between the downhole pump assembly and the pumpseating nipple 10, thereby holding the downhole pump assembly in a fixedposition despite forces imparted by the movement of the plunger 122. Inone embodiment, when the downhole pump assembly is fixed in position bythe pump seating nipple 10, the openings 30 are positioned above theperforated fitting 112 of the barrel 114.

In the event that any of the seating cups 116 is advanced below theupper portion 24 of the nipple bore 20, upon upward pulling of thedownhole pump assembly, the seating cups 116 will be guided andcompressed by the lower chamfer 34 to facilitate upward movement of thedownhole pump assembly into the upper portion 24 of the nipple bore 20.

In use, the elevation of the production fluid F within the productionbore 103 is preferably maintained at a level between the perforatedfitting 112 of the pump assembly, and the openings 30 of the pumpseating nipple 10. As shown by the solid arrow lines in FIG. 2, theproduction fluid F flows from the perforated zone of the formation intothe relatively low pressure environment of the production bore 103.Dissolved gases in the production fluid F may break out of solution inthe production bore 103 and rise to the level of the production fluid Fwithin the production bore 103, where they are liberated. The liberatedgases flow into the lower skirt 28, where further upward flow isprevented by the sealing relationship between the seating cups, the pumpassembly and the upper portion 22 of the inner surface 18. Accordingly,the gases in the lower portion 28 of the nipple bore 20 flow through theopenings 30 and into the casing annulus 105, where they may rise freelyup towards the ground surface. In this manner, gas pressure which mayevolve during pump seating may be relieved. This may encourage the gasesto breakout of solution from the production fluid F and thus reduce theamount of dissolved gas that flows into the pump barrel 114 through thestanding valve. Accordingly, the pump seating nipple 10 of the presentinvention may be used to help avoid gas locking phenomenon associatedwith a downhole reciprocating pump system 100.

As will be apparent to those skilled in the art, various modifications,adaptations and variations of the foregoing specific disclosure can bemade without departing from the scope of the invention claimed herein.

What is claimed is:
 1. A pump seating nipple for retaining a pumpassembly in a fixed and sealed position within a production tubingstring disposed within a casing string to define a casing annulustherebetween, the pump seating nipple being insertable in the productiontubing string and comprising: a substantially cylindrical body defininga nipple bore extending from a top end of the body to a bottom end ofthe body, wherein the body comprises an upper portion for receiving thepump assembly at least partially therein and a lower skirt which has aninside diameter larger than the pump assembly and which defines at leastone opening extending through the lower skirt for fluid communicationfrom the nipple bore to the casing annulus.
 2. The pump seating nippleof claim 1 wherein the top end defines a top threaded surface forremovable attachment of the top end to the upper joint, and the bottomend defines a bottom threaded surface for removable attachment of thebottom end to the lower joint.
 3. The pump seating nipple of claim 1wherein the body defines a chamfer between the top end of the body andan upper portion of an inner surface.
 4. The pump seating nipple ofclaim 1 wherein the lower skirt has an internal diameter larger than theinternal diameter of the upper portion of the body.
 5. The pump seatingnipple of claim 4 wherein the body defines a chamfer between the insidediameter of the upper portion and the inside diameter of the lowerskirt.
 6. The pump seating nipple of claim 1 wherein the at least oneopening comprises a plurality of openings arranged in a plurality ofcolumns or rows circumferentially spaced apart on the body.
 7. Adownhole assembly adapted to be disposed within a casing string andcomprising: (a) a production tubing string defining a production boreand disposed within the casing string to define a casing annulustherebetween; (b) a downhole pump assembly disposed within theproduction bore comprising a barrel with a perforated fitting for fluidcommunication from the production bore into the barrel, and an attachedresilient annular seating cup; (c) a pump seating nipple disposed in theproduction tubing string, the pump seating nipple comprising asubstantially cylindrical body comprising an outer surface, and an innersurface defining a nipple bore extending from a top end of the body to abottom end of the body for receiving the downhole pump at leastpartially therein, wherein the nipple bore is in fluid communicationwith the production bore at the bottom end of the body; wherein theinner surface comprises an upper portion to engage the seating cup toresist relative movement between the downhole pump assembly and the bodyand to prevent gas migration between the downhole pump assembly and thebody; and wherein the body comprises a lower skirt having an insidediameter greater than a pump outside diameter and which defines at leastone opening extending from a lower portion of the inner surface to theouter surface for fluid communication from the nipple bore to the casingannulus, wherein the at least one opening is disposed above theperforated fitting.